Saving Energy in Existing Multifamily Buildings Duluth Energy Design Conference February, 2016 Corrie Bastian Center for Energy and Environment
Saving Energy in Existing Multifamily Buildings
Duluth Energy Design Conference February, 2016
Corrie Bastian Center for Energy and Environment
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Topics
• Who is CEE • Energy use in multifamily buildings • Perspective: Understanding the industry • Retrofit highlights
• Energy impact • Marketability • Ensuring success: I, O & M best practices
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Who is CEE
The Center for Energy and Environment (CEE) is a nonprofit organization that promotes energy efficiency to strengthen the economy while improving the environment We conduct research and develop programs so that:
• Businesses operate more efficiently and profitably; • Government agencies and nonprofits spend less on facilities
and functions; • Utilities achieve their energy-efficiency goals at least-cost; and • Households save money and improve comfort.
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What we do
• Energy Program Design and Delivery • Engineering Services • Public Policy • Lending Center • Innovation Exchange
• Research • Education and Outreach
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CEE multifamily experience
• Facility assessments of over 2,000 buildings in Minnesota
• Completed over 20 research projects
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Current multifamily research projects
• Condensing boiler optimization • Multifamily ventilation optimization • Demand Controller recirculation loop controls • Multifamily aerosol envelope air sealing • Indoor pool optimization
All funded through the MN Department of Commerce’s Conservation Applied Research and Development grant program.
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Current multifamily energy efficiency programs
• Energy Star multifamily 3rd party verifier • One Stop Efficiency Shop lighting program with
Xcel Energy • Multifamily Energy Savings program with
MN Energy Resources
Understanding multifamily buildings
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What we know about multifamily buildings
“Multifamily buildings are a tough energy efficiency nut to crack”
Why? • “Split incentive” / diverging interests between
resident and owner • “Lots of players in the orchestra” • Perception that technical challenges outweigh
financial benefits
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Market research on multifamily building owners and managers reveals perceptions of energy efficiency
• “Expensive” • “Complex maintenance and upkeep” • “Realized savings are questionable” • “Improved comfort is a big benefit” • “Has to be durable” • “Trustworthy energy
efficiency advice is needed”
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MN multifamily buildings are relatively “fit” buildings
SOURCE:MinnesotaMulDfamilyRentalCharacterizaDonStudy,EnergyCenterofWisconsinandFranklinEnergy,2013;sampled120bldgsinMN(78inTwinCiDes,66GreaterMN)
• Natural gas = common
heating fuel (~66%) • Central hydronic =
common heat system (83%)
4-6BTU/`2/HDD
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…And yet outliers in (almost) every category
SOURCE:MinnesotaMulDfamilyRentalCharacterizaDonStudy,EnergyCenterofWisconsinandFranklinEnergy,2013;sampled120bldgsinMN(78inTwinCiDes,66GreaterMN)
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Water and space heating costs dominate
SOURCE:MinnesotaMulDfamilyRentalCharacterizaDonStudy,EnergyCenterofWisconsinandFranklinEnergy,2013;sampled120bldgsinMN(78inTwinCiDes,66GreaterMN)
=40%
=15%
=10%
=34%
Average Multifamily Utility Costs (per unit / year)
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…And yet they are a small piece of the expense pie
Payroll&Benefits19%
Insurance4%
Taxes17%
MgmntFee8%
Admin4%
Water&
Sewer5%
Elec.3%
Gas4%
Trash,Cable,Misc.4%
Repairs27%
MarkeUng2%
Other3%
UUliUes=12%
Source:2013MNMul*HousingAssocia*onExpensesurvey.388mulDfamilyproperDessurveyed
Average MN Multifamily operating expenses
A good investment…
q Has aggressive energy paybacks
q Lowers O & M costs q Improves building comfort q Makes things easier for staff q Is “tried and true” q Is easy to implement
i.e. Energy efficiency marketability goes well beyond payback
Marketable energy efficiency strategies for MN multifamily
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Good opportunities for energy savings – beyond “the laundry list”
• Optimizing existing condensing boilers • Building ventilation modifications • Demand-based hot water recirculation loop controls • Aerosol envelope air sealing
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Acknowledgements
Projects discussed are supported in part by a grant from the Minnesota Department of Commerce, Division of Energy Resources through a Conservation Applied Research and Development (CARD) program
Optimizing condensing boilers
Conventional boiler
ßSupply
ßReturn
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Condensing boiler
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Achieving rated efficiency (>90% efficiency)
CONDENSINGTEMPS
Return water temperature
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Condensing?
Benefits
• 4-10% of gained efficiency • Eliminate short-cycling • Getting what you paid “extra” for
THE KEY: Driving down return water temperature
• Maximize heat transfer at heating elements • Send lower temp water out to the building • Make sure boiler output matches demand • Make sure your piping isn’t dumping supply water into
return • Make sure domestic hot water is not integrated with
space heating boiler
How?
• Considerations for an existing condensing system • Proper excess air levels • Adjusting outdoor reset and sequencing/staging controls • Reducing maximum output temp • VFD pumping for increased heat transfer
• OR Considerations at time of replacement • Boiler room piping • Choosing a boiler with good on board reset and sequencing/
staging controls
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Excess air can dictate boiler efficiency
Imagesource:industrialheaDng.com
A
DJU
STM
ENT
RA
NG
E
Measured as % Oxygen in flue gas
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Condensing boiler sensitivity to excess air
• Controlling excess air very important • Excess air reduces concentration of
water vapor • Dewpoint decreases
LowExcessAir
HighExcessAir
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Oxygen levels in flue gas
Heating elements: You’re stuck with them • It isn’t cost effective to add more • Dirty or blocked radiation affects heat transfer
Control boilers for lowest possible output
• Optimized outdoor reset • Finding the lowest max output temp for the building • Sequencing and staging for optimal efficiency
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Control the boiler so it doesn’t exceed demand
20°F in March
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Outdoor reset lowers boiler water temperature As outdoor temps get warmer, the building heating load gets smaller and the boiler water
temperature can be lowered.
-20°F
0°F
20°F
40°F
60°F
80°F
100°F
120°F
140°F
160°F
180°F
Boilerwatertemperaturewithoutdoorreset
Space75°F
Boilerwatertemperature,nocontrol
Optimizing outdoor reset
MinOATforcondensingmovedfrom34°Fto22°FCanyougolower?
Boilerw
aterte
mp
OutdoortempAdjustedsupplycurve
Adjustedreturncurve
Outdoor reset adjustment
14 unit building: 9.5% space heating savings (no cost) Reduced building over-heating
At replacement: Identify boiler control limitations • This boiler control’s non-adjustable minimum outside
temp of 0°F is not ideal for MN
Boiler sequence and firing stage controls: matching output to load for best efficiency
Loweroutputfiringstageshaveincreasedthermalefficiency
Imagesource:Lochinvar.com
Lochinvar Knight boiler cascade strategies:
Imagesource:lochinvar.com
Sequencing boilers: mixed efficiency
41 unit building: 11% space heating savings 3 year payback Reduced short-cycling
Sequencing/staging: All firing on at once because they can’t talk to each other
32 unit building: 6% space heating savings 5 year payback Reduced short-cycling
Variable speed pumps (VFDs, VSDs)
• Reduce the pump flow during part-load (when zones close)
• Allows for lowered return water temperature—more potential boiler condensing conditions
• Electricity savings
Little difference between boiler supply and return temperatures indicates potential for improvement
1- Adjust reset temps as low as possible 2- VFD pump control optimizes heat transfer as zones
open and close
Boiler room piping: address at replacement
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2
3
4
RETURNBuildingloop
Not ideal: Adjacent boilers warm return water
Better piping
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